In the conventional liquid display 1 as shown in FIG. 1, the first substrate 10 has a first electrode 11, the second substrate 30 has a second electrode 31, and a liquid crystal layer 20 is disposed between the first electrode 11 and the second electrode 31. The protrusion 12 disposed on the first electrode 11 can divide each pixel area into a plurality of domains. So, each liquid crystal molecules 21 is not vertical but has an angle to the first substrate 10, called multi-domain vertical alignment (MVA). As such, the view angle of a user is increased.
However, the manufacture of the protrusion 12 is difficult so the cost of the conventional display 1 is very high and is easy to malfunction.
The other conventional liquid crystal display 4 is shown in FIGS. 2-1 and 2-2. FIG. 2-1 is a cross-sectional view of another conventional liquid crystal display. And FIG. 2-2 is a top view of the conventional liquid crystal display as shown in FIG. 2-1. The first substrate 40 has a first electrode 41. The second substrate 60 has a plurality of second electrodes 62 each of which further has sub-electrodes 62′ divided by the slit 62a. A third electrode 63 is disposed under the slit 62a so the liquid crystal molecules 51 of the liquid crystal layer 50 is always parallel to the first electrode 41. And the other liquid molecules 52 have an angle to the first electrode 41. The second electrode 62 and the third electrode 63 are disposed separately by insulating film 61.
However, as shown in FIG. 3, the liquid crystal molecules 53 far from the third electrode 63 is pointed to the third electrode 63. But when an electric field is present across between the first and second substrates 40 and 60, the liquid crystal molecules 51 above the slit 62a are tilted and flow along the longitudinal direction of the third electrode 63 first, and after a period of time, the liquid crystal molecules 51 then rotate as the liquid crystal molecules 53. It causes the slow responding time.
Another problem is that the liquid crystal molecules 52 above the edge 63′ of the third electrode 63 will rotate suddenly because of the electric field resulting from the overlapping of the second electrode 62 and third electrode 63. The unstable states of the liquid crystal molecules 52 not only cause the slow responding time but also cause the flicker of the liquid crystal display 4.
And yet another problem is that when the conventional liquid crystal display wants to increase the transmittance, the pixel voltage must be increased relatively. Generally speaking, the transmittance is raised while the pixel voltage is (of the sub-electrode 62′) raised. Please refer to the FIG. 2-1. However, when the pixel voltage gets closing to the value of the bias voltage (of the third electrode 63), the transmittance gets going down because the liquid crystal molecules 55′ rotate reversely and block the light which passes through the liquid crystal layer 50. In the FIG. 2-1, when the pixel voltage (of the sub-electrode 62′) gets higher, because of the reverse area 55, the reversely rotating molecules 5′ is created. Then the liquid crystal molecules 55′ collide with the liquid crystal molecules 53′ in the normal area 53 and then a colliding area 57 is created. Therefore, the transmittance of the conventional liquid crystal display are decreased by the colliding area 57. And the importance of controlling the voltage interval between the sub-electrode 62′ and the third electrode 63 is also described below.